Didn't the "tokens backed by something off-chain, and then a fork happens" already happen with Digix?

I believe they just basically said "we are treating the tokens on Ethereum, not on Ethereum Classic, as being the ones which are redeemable". I don't see what the problem with this is. It is inconvenient for the people who prefer to use Ethereum Classic, yes, but they didn't lose their tokens. They still have control of those tokens on the Ethereum (ETH(F)) chain, and can sell those if they want to end up only using Ethereum Classic.

This is unfortunate for them, and if this inconvenience could be avoided for free, then that would be better, but I don't think it is unfair to them. They still have the same control over the same tokens that are accepted as legitimate as they did before.